It is standard to provide a recipient, hereinafter referred to as a bottle, with a cap that is constructed so that once it is sealed the cap can only be removed by permanently damaging or deforming an element of the closure, thereby signaling to the consumer that the package has been tampered with. Such an arrangement is particularly needed on a screw-type closure that could otherwise be reclosed and appear to never have been opened in the first place.
A standard such configuration has a cap formed as an internally threaded cup having a rim connected via a low-strength integral web with a so-called tamper ring. The ring is provided with a sawtooth formation or lip directed upward toward the cap and is molded as a single unitary element with the cap. In such an arrangement once the assembly is screwed down over the opening of the bottle the sawtooth formation or lip snaps into a groove and strongly blocks reverse upward displacement of the cap. Thus when the cap is screwed off the frangible web connecting the cap to the ring ruptures, leaving behind the desired evidence that the container has been opened.
The main difficulty with such an arrangement is that several different needs must be satisfied by the material of the closure. The cap must seal tightly, the ring must hold solidly on the bottle, and the frangible web must resist enough to avoid damage prior to assembly, must be readily severable by the consumer, and must not deform enough to move off the bottle without permanent damage. It is therefore necessary to trade off the various advantages and disadvantages against one another. The result is therefore an assembly made of a resin that is not well adapted to all the tasks at hand. In addition when the ring and cap are unitary they must be of the same color, making it impossible to use differently colored rings and caps to distinguish different products or just for design purposes.
In French patent 7,439,911 I describe a system with a cap that is separate from the tamper ring. Here the tamper ring snaps into an inwardly open groove in the cap in the same manner it snaps into an outwardly open groove in the bottle neck. Between the two ends of the ring, one end fixed axially in the cap and the other on the bottle by their respective sawtooth formations or lips, the ring is formed with a frangible web intended to rupture, leaving half the ring on the cap and half on the bottle when the closure is first opened. In this arrangement the cap is made of a rigid synthetic resin such as high-density polyethylene and the ring is made of a more supple resin, such as low-density polyethylene so that it can be torn easily.
Such an arrangement overcomes some of the disadvantages of the one-piece system, but has been found not to be applicable to certain products. Medicines in particular must often be packed extremely tightly, so that the cap must include a relatively soft plug that will seal the bottle hermetically. Such a closure therefore has three parts and is so expensive to manufacture, requiring a removable-core mold, that it can only be used with relatively expensive products.